Hummer H2. Manual - part 779

illuminated.  

28.  

If the brake system warning light remains illuminated, see BRAKE WARNING INDICATOR 
ALWAYS ON under SYMPTOM TESTS.  

MASTER CYLINDER RESERVOIR FILLING 

1. Visually inspect the brake fluid level through the brake master cylinder reservoir.  

2. If the brake fluid level is at or below the half-full point during routine fluid checks, the brake system 

should be inspected for wear and possible brake fluid leaks.  

3. If the brake fluid level is at or below the half-full point during routine fluid checks, and an inspection of 

the brake system did not reveal wear or brake fluid leaks, the brake fluid may be topped-off up to the 
maximum-fill level.  

4. If brake system service was just completed, the brake fluid may be topped-off up to the maximum-fill 

level.  

5. If the brake fluid level is above the half-full point, adding brake fluid is not recommended under normal 

conditions.  

6. If brake fluid is to be added to the master cylinder reservoir, clean the outside of the reservoir on and 

around the reservoir cap prior to removing the cap and diaphragm. Use only Delco Supreme 11(R) (GM 
P/N 12377967), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.  

HYDRAULIC BRAKE SYSTEM FLUSHING 

CAUTION: DO NOT allow the vehicle to be driven until it is diagnosed and 

repaired. 

WARNING:

Brake fluid may irritate eyes and skin. In case of eye contact, rinse 
thoroughly with water. In case of skin contact, wash with soap and water. 
In case of ingestion, consult a physician immediately. 

CAUTION: Avoid spilling brake fluid onto painted surfaces, electrical connections, 

wiring, or cables. Brake fluid will damage painted surfaces and cause 
corrosion to electrical components. If any brake fluid comes in contact 
with painted surfaces, immediately flush the area with water. If any brake 
fluid comes in contact with electrical connections, wiring, or cables, use a 
clean shop cloth to wipe away the fluid. 

CAUTION: When adding fluid to the brake master cylinder reservoir, use only Delco 

Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a 
clean, sealed brake fluid container. The use of any type of fluid other than 
the recommended type of brake fluid, may cause contamination which 
could result in damage to the internal rubber seals and/or rubber linings of 
hydraulic brake system components. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

1. Inspect the brake fluid for the following conditions, indicating brake fluid contamination: 

A. Fluid separation indicating 2 types of fluid are present; a substance other than the recommended 

brake fluid has been introduced into the brake hydraulic system: 

z

If its a swirled appearance, then it is an oil-based substance.  

z

If its a layered appearance, then it is a silicone-based substance.  

B. Fluid discoloration, indicating the presence of moisture or particles that have been introduced into 

the brake hydraulic system: 

z

If its a cloudy appearance, then its due to moisture.  

z

If its a dark appearance/suspended particles in fluid, then its due to dirt, rust, corrosion, brake 
dust.  

2. Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for 

swelling, indicating brake fluid contamination.  

3. If the brake fluid was contaminated with an oil-based or a silicone-based substance, indicated by fluid 

separation and/or a swollen master cylinder reservoir cap diaphragm and/or swollen reservoir-to-master 
cylinder grommets, perform the following: 

A. Remove all of the following components listed from the vehicle. Each component contains internal 

rubber seals/linings which have been contaminated by the contaminated brake fluid in the brake 
hydraulic system. Refer to the procedures indicated: 

z

Replace master cylinder. See MASTER CYLINDER under REMOVAL & 
INSTALLATION.  

z

Replace appropriate brake hose. See BRAKE HOSE under REMOVAL & 
INSTALLATION.  

z

Replace appropriate brake hose. See BRAKE CALIPER under REMOVAL & 
INSTALLATION.  

z

Replace Brake Pressure Modulator Valve (BPMV). See appropriate ANTI-LOCK article. 

WARNING:

Brake fluid may irritate eyes and skin. In case of eye contact, rinse 
thoroughly with water. In case of skin contact, wash with soap and water. 
In case of ingestion, consult a physician immediately. 

CAUTION: Avoid spilling brake fluid onto painted surfaces, electrical connections, 

wiring, or cables. Brake fluid will damage painted surfaces and cause 
corrosion to electrical components. If any brake fluid comes in contact 
with painted surfaces, immediately flush the area with water. If any brake 
fluid comes in contact with electrical connections, wiring, or cables, use a 
clean shop cloth to wipe away the fluid. 

CAUTION: When adding fluid to the brake master cylinder reservoir, use only Delco 

Supreme 11(R) (GM P/N 12377967), or equivalent DOT-3 brake fluid from a 
clean, sealed brake fluid container. The use of any type of fluid other than 
the recommended type of brake fluid, may cause contamination which 
could result in damage to the internal rubber seals and/or rubber linings of 
hydraulic brake system components. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

B. Clean out all the hydraulic brake pipes using denatured alcohol (or equivalent).  

C. Dry the brake pipes using non-lubricated, filtered air.  

D. Repair or replace ALL of the following components listed and install them to the vehicle. Each 

component contains internal rubber seals/linings which have been contaminated by the 
contaminated brake fluid in the brake hydraulic system. Refer to the procedures indicated: 

z

See MASTER CYLINDER under OVERHAUL; or see MASTER CYLINDER under 
REMOVAL & INSTALLATION. Clean the brake master cylinder reservoir using denatured 
alcohol (or equivalent), then dry the reservoir using non-lubricated, filtered air. Inspect the 
reservoir for cracks and/or damage and replace if necessary. See MASTER CYLINDER 
RESERVOIR under REMOVAL & INSTALLATION. Replace the brake master cylinder 
reservoir cap diaphragm.  

z

See BRAKE HOSE under REMOVAL & INSTALLATION.  

z

See BRAKE CALIPER under OVERHAUL; or see BRAKE CALIPER under REMOVAL 
& INSTALLATION.  

z

Replace Brake Pressure Modulator Valve (BPMV). See appropriate ANTI-LOCK article.  

4. If the brake fluid was not contaminated with an oil-based or a silicone-based substance, but was 

contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the brake master cylinder 
reservoir cap diaphragm which may have allowed the moisture or particles to enter the hydraulic system.  

5. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11(R) (GM P/N 

12377967), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.  

6. Pressure bleed the hydraulic brake system; begin the procedure with the pressure bleeder reservoir filled 

to the maximum-fill level with the correct brake fluid as indicated. See MANUAL BLEEDING or 
PRESSURE BLEEDING .  

ADJUSTMENTS & INSPECTION 

BRAKE ROTOR THICKNESS MEASUREMENT 

1. If the inboard friction surface of the brake rotor is not accessible, reposition and support the caliper with 

the brake pads. See BRAKE PADS under REMOVAL & INSTALLATION.  

2. Clean the brake pad lining contact surface of the brake rotor with denatured alcohol or an equivalent 

brake cleaner.  

3. Using a calibrated micrometer, measure and record the lowest thickness of the brake rotor at 4 or more 

points, equally spaced around the rotor. See Fig. 2 . Ensure that the measurements are only taken within 

CAUTION: Avoid grinding brake linings, sanding brake linings or cleaning wheel 

brake parts with a dry brush or with compressed air, when servicing wheel 
brake parts. Some models or aftermarket brake parts may contain 
asbestos fibers which can become airborne in dust. Breathing dust with 
asbestos fibers may cause serious bodily harm. Use a water-dampened 
cloth in order to remove any dust on brake parts. Equipment is available 
commercially in order to perform this washing function. These wet 
methods prevent fibers from becoming airborne. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer

  

the brake pad lining contact area and that the micrometer is positioned the same distance from the outside 
edge of the rotor for about 1/2" (13 mm), for each measurement.  

4. Compare the lowest thickness measurement recorded to the rotor minimum allowable thickness after 

refinishing and the rotor discard thickness specifications. See DISC BRAKE SPECIFICATIONS .  

5. If the lowest thickness measurement of the brake rotor is above the minimum allowable thickness after 

refinishing specification; the rotor may be able to be refinished, depending upon surface and wear 
conditions which may be present. See BRAKE ROTOR REFINISHING under OVERHAUL.  

6. If the lowest thickness measurement of the brake rotor is at or below the minimum allowable thickness 

after refinishing specification, the rotor may not be refinished.  

7. If the lowest thickness measurement of the brake rotor is at or below the discard thickness specification 

then the rotor requires replacement. See BRAKE ROTOR under REMOVAL & INSTALLATION. 

 

2004 Hummer H2 

2003-04 BRAKES Disc - Hummer